The present invention relates to a diagnosis system for internal combustion engines, and more particularly to a system for diagnosing failure of a starter operation switch of an engine mounted on a motor vehicle and for displaying its failure.
An electronic fuel-injection system of the type which is provided with a computer to compute various factors such as starter operation, throttle position, volume of intake airflow, intake manifold vacuum and coolant temperature in order to produce output signals for driving solenoid-operated fuel injector is known. The starter operation switch is provided to produce a starter signal, when a starter for the engine is operated. At cold engine, air-fuel mixture is enriched by the starter signal and coolant temperature signal. If trouble occurs in the starter operation switch system, the starter signal is not applied to the computer. Consequently, the control operation for the fuel injector is not properly carried out, resulting in failure of engine starting. In order to avoid such failure, a fail-safe operation system should be provided to ensure the starting of the engine, even if the starter signal is not fed to the computer. Further, a warning system for the failure of the starter operation switch system must be provided. However, if the driver of the vehicle does not notice the warning of the failure during the starting of the engine, the warning is not given to the driver until the subsequent starting of the engine. Since the sensor system is left in failure, the engine may not be started the next time.